The present invention relates to control cables and, more particularly, to a novel cable-like device which transmits one-way compression forces in a first direction and zero force in the reverse direction.
A number of different types of control cables have been used through the years. In the engine throttle control area, for example, cables having an outer tube and an inner braided metallic cord are common for linkage between an accelerator pedal and a carburetor, fuel injector body or the like. Such cables, which are generally tension or pull only type devices, tend to be high friction devices in the throttle closing direction.
Throttle sticking is a problem sometimes encountered with this type of cable. Generally, such sticking occurs at low speeds because friction loads on the throttle bearings are at maximum under this condition, often aggravated by the fact that the throttle return spring has less effect at the extremes of throttle displacement due to the shorter effective moment arm of the usual pivoting lever actuator in these positions. This friction in combination with that of the cable, in the presence of possible reduced spring return forces, can cause the vehicle minimum speed to exceed 25 m.p.h. One way to overcome such sticking is to increase the spring force of the throttle return spring, however, this can cause the phenomenon referred to as "cyclic driving".
Cyclic driving occurs when a strong throttle return spring exerts an excessive force on the throttle cable which, in turn, exerts an excessive force on the accelerator pedal. As an operator is driving a vehicle, this high pedal return force, caused by the strong throttle return spring, pushes against the operator's foot and progressively causes it to raise, thereby causing the vehicle to progressively slow down. When the operator eventually realizes that he has slowed down, he pushes the accelerator pedal back down to increase the vehicle speed back to normal. The cycle then repeats. This repeated slowing and speeding up process is known as cyclic driving.
Another more serious problem, which applicant believes is associated with throttle linkage or cable sticking, is "vehicle run-away". Applicant believes this occurs in accordance with the following scenario. The vehicle engine is operating at a curb idle when the automatic transmission is placed in gear. The transmission drag reduces the engine idle speed which causes the idle control to crack open the throttle to restore the engine to a normal idling speed. This cracking open of the throttle increases air flow in the engine causing a leaner mixture of the fuel/air ratio. The fuel injection system of the vehicle, in an attempt to restore the proper fuel/air ratio, increases the fuel supply causing the engine to flood and begin to stall. The driver, in an attempt to overcome the flooding, vigorously steps on the accelerator pedal to open the throttle further to prevent the engine from stalling. As the engine flooding condition clears, the vehicle takes off at near full throttle. The driver removes his foot from the accelerator pedal, but the throttle linkage or cable sticks or responds slowly and a vehicle run-away condition exists.
A primary object of the present invention resides in the provision of an improved cable, and particularly an improved throttle cable, that has negligible friction in the return direction thereby enabling the cable to rapidly and reliably return to its original position, thus substantially eliminating the aforesaid problems associated with throttle sticking. Also, the present invention enables the use of a throttle return spring with a reduced spring force, thereby minimizing the chance of cyclic driving.
From the subsequent description and appended claims taken in conjunction with the accompanying drawings, additional features and advantages of the present invention will become apparent to those skilled in the art.